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Should be fixed at long last in commit 3a90241189112af13937c37e9f94363e6c7708ef. A secondary problem, of the build's proceeding even after m4 fails, should also be fixed in commit 08d269fc89eb5962c29772b2fe41ae15a58b11c0.

I was trying to bootstrap MIT/GNU Scheme on Debian GNU/Hurd by compiling from src/microcode in the latest snapshot and I noticed on my own that I didn't have m4 installed. The build system never complains about the missing dependency, nor does GCC complain that its receiving empty assembly source files. One does get a lot of "undefined references" from GCC when linking occurs.

This gave me the opportunity to check out all the assembly code for MIT Scheme written in stunning m4.